The invention relates to a stirrer for a stirrer vessel, which stirrer comprises a stirrer head, a drive unit and a magnetic coupling, wherein the magnetic coupling has drive magnets connected to the drive unit and stirrer head magnets connected to the stirrer head, wherein the stirrer head has stirrer blades and a bearing assembly, and wherein the stirrer blades are connected to the stirrer head magnets and the bearing assembly, wherein the bearing assembly rotatably supports the stirrer head and the bearing assembly comprises a first rotational bearing.
Stirrers for stirrer vessels are used, e.g., in the biopharmaceutical industry, the food industry and in particular in the field of aseptical liquid production processes. Typical configurations of such stirrer vessels are gas-tight and closable tank-like vessels made from metal or glass, which ensure simple cleaning and sterilization and, hence, multiple use. Mixing a stirring medium contained in the stirrer vessel is realized within the stirrer vessel by means of a stirrer head, which has stirrer blades and which is connected to a stirrer shaft having stirrer shaft blades arranged thereon, depending on the application and configuration of the stirrer vessel. In common stirrers, the connection of the drive unit with the stirrer head is realized via a sliding ring sealing. Stirrers sealed via sliding ring sealings, however, do have the disadvantage that leakage at the sealing may occur. Furthermore, maintenance of this type of sealing is work and cost intensive, wherein leaking in the case of correct maintenance is only minimal. In the pharmaceutical field and the food industry, however, this leakage and the contamination associated therewith of the stirring medium do constitute a high risk. For this reason, these industries have increasingly made use of stirrers having magnetic coupling, which are also termed magnetic stirrers, instead of stirrers having sliding ring sealings. Supporting the stirrer head of such stirrers is realized via a rotational bearing such as, e.g., a slide bearing.
EP 1 748 201 B1 discloses a stirrer having a magnetic coupling between drive unit and stirrer. It further comprises a rotational bearing in the form of a slide bearing, which is lubricated by the stirring medium within the vessel.
With such constructions it has proven to be disadvantageous that the rotational bearing limits the torque applied by the drive unit, the maximum rotational frequency, and the size of the stirrer blades as well as the length of the stirrer shaft. Improving these characteristics will lead to increased vibrations on the stirrer head and, as a consequence, to mechanical damage.